The present invention relates to tank pressure control systems and particularly to an apparatus for controlling flow of fuel vapor and liquid fuel through an aperture in a fuel tank. More particularly, the present invention relates to a fill-limit valve system for controlling tank ventilation and for preventing overfilling of a vehicle fuel tank.
Fuel-dispensing pump nozzles are known to include a fill-limiting sensor for shutting of the flow of fuel from the nozzle when a vehicle fuel tank is nearly filled. Typically, this fill-limiting sensor is triggered whenever the fuel tank is full and fuel "backs up" the tank filler neck to splash onto or reach the fill-limiting sensor located on the nozzle. Sometimes fuel pump operators overfill a fuel tank inadvertently in a good-faith effort to fill the tank "completely" or to purchase a quantity of fuel that can be paid for in cash without causing the operator to receive unwanted coinage in change.
It has been observed that fuel pump operators are able to manually override or bypass some fill-limiting sensors on nozzles by continuing to pump fuel after the pump nozzle has automatically shut off several times. This practice has come to be called the "trickle-fill" method of introducing liquid fuel into a fuel tank. Using this well-known trickle-fill method, the fuel pump operator "clicks" or squeezes the lever handle on the pump nozzle slowly two or three times in succession after automatic nozzle shut-off has occurred in order to introduce more fuel into the fuel tank without actuating the fill-limiting sensor right away. It will be appreciated that such trickle-fill practices can result in overfilling the fuel tank which can effectively reduce the fuel vapor expansion capacity in the vapor space available within the filled fuel tank.
During cornering, the liquid fuel inside a vehicle fuel tank is often agitated to cause the liquid fuel to move with a splashing motion inside the vehicle fuel tank. Liquid fuel can also be sloshed about in a vehicle fuel tank in response to other types of vehicle motion in addition to vehicle cornering.
Vehicle fuel tanks include vent apparatus for regulating discharge of liquid fuel and fuel vapor from the interior region of the fuel tank. Such a vent apparatus is often mounted in an aperture formed in a top wall of the vehicle fuel tank and could be exposed to rising levels of liquid fuel in the fuel tank during refueling and/or to agitated liquid fuel that is sloshed about inside the vehicle fuel tank during cornering or other movement of the vehicle. This type of vent apparatus often includes a buoyant "float valve" that is movable in a fuel tank to open and close a fuel tank venting outlet and that is capable of floating in liquid fuel once the liquid fuel rises to a certain level in the fuel tank. During tank refueling and sometimes during fuel sloshing, float valves are moved by liquid fuel to close tank venting outlets.
According to the present invention, an apparatus is provided for controlling the discharge of fuel vapor and liquid fuel through an aperture in a fuel tank. The apparatus includes a housing formed to include a venting outlet, a vent valve positioned to lie in the housing, and a valve actuator coupled to the vent valve. The vent valve moves between an opened position allowing flow of fuel vapor in the tank through the venting outlet formed in the housing and a closed position preventing flow of fuel vapor and liquid fuel in the tank through the venting outlet. The valve actuator includes an electronic liquid detector and is operable to move the vent valve to the closed position upon detection of liquid fuel that has been communicated to the valve actuator due to, for example, filling the tank to its fill limit with liquid fuel and/or sloshing of liquid fuel inside the tank.
In preferred embodiments, the valve actuator includes a vent valve mover and the electronic liquid detector is coupled to the vent valve mover. The vent valve mover is positioned to lie in the housing and arranged to move the vent valve between the opened and closed positions. The electronic liquid detector includes a valve mover controller coupled to the vent valve mover and an electronic sensor coupled to the valve mover controller. The electronic sensor senses the presence of liquid fuel at a predetermined region or position in the fuel tank (e.g., in the lower region of an open bottom portion of the housing exposed to fuel vapor and liquid fuel in the interior region of the fuel tank). When the electronic sensor senses liquid fuel at the predetermined position, the valve mover controller instructs the valve mover to move the valve to the closed position. The electronic sensor is preferably either a capacitance sensor or an optical sensor and the valve mover controller preferably includes a solenoid.
Additional features of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.